1. Field of the Invention
The present invention relates to battery charging methods and devices, and in particular to methods and devices for charging batteries using an unstable power source.
2. Description of the Related Art
Following the recent trend of consumers being more environmentally conscious, the application of green energy or renewable energy such as wind power, solar energy, hydro power, and tidal power, has attracted great attention. The features of green energy sources are inherently unstable, however. Generally, green energy is transformed into electric power for storage, thereby enhancing the utilization efficiency of green energy.
Typical battery charging methods, such as Constant Voltage Charging (CV Charging), Constant Current Charging (CC Charging), Pulse Charging, and Reflex Charging, are based on having a stable power source as a charging source. The progress of the battery charging is determined through sampling voltage or current from the battery under charge. However, when these battery charging methods are performed using an unstable power source, the floating charge voltage of the battery will drift with the unstable power source, resulting in a variation of the sampling result from the battery and thus the risk of misjudging the battery charging progress. Taking wind power for instance, the charging current generated by the wind-driven generator is proportional to the wind power, and variations in the wind makes the charging current unstable, resulting in voltage drift in the battery under charge due to the battery's resistance. If the voltage or current of the battery is sampled directly during charging, misjudgment of the charging level of the battery may occur due to the instability of wind power. Thus, a method and device for charring batteries using unstable power sources are desired in order to enhance the utilization efficiency of green energy sources.